<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script src="http://ajax.aspnetcdn.com/ajax/jQuery/jquery-1.8.0.js"></script>
</head>
<script>
    $(document).ready(function() {
        $('#user').blur(function() {
            $.post('./jquery.php', {
                uservalue: $('#user').val(),
                pwd: $('#pwd').val()
            }, function(data, statu) {
                $('#info').html(data)
            });
        })
    })
</script>

<body>
    <form>
        用户名：<input type="text" id="user" name="username">
        <span id="info"></span></span>密码：
        <input type="password" name="" id="pwd">
        <input type="button" name="" value="注册" id="btn">
    </form>
</body>

</html>